The electrochemical double layer at the graphene/aqueous electrolyte interface: what we can learn from simulations, experiments, and theory

Abstract

The physical-chemistry of the graphene/aqueous-electrolyte interface underpins the operational conditions of a wide range of devices. Despite its importance, this interface is poorly understood due to the challenges faced in...

Intrinsic Interface Adsorption Drives Selectivity in Atomically Smooth Nanofluidic Channels

“…Figure (b) shows the equilibrium particle number densities, ρ i ( z ) for water, potassium, and chloride, with i = {w, K + , Cl – }, in the BN and GR channels, relative to their bulk values, ρ̅ i . We observe similar structures in both materials with interfacial layering of water that is consistent with previous simulations of neat water. , The distribution of ions near such interfaces is known to be highly dependent on ion species, and the profiles shown are consistent with previous simulations. − A dense layer of pure water accumulates near the wall, with the molecules oriented such that they induce a small local negative charge. The next layers are enriched in alternating concentrations of potassium and chloride ions, with depletion (accumulation) of water molecules accompanying potassium (chloride) enrichment.…”

Anion Intercalation into Graphite Drives Surface Wetting

“…The first experimental evidence of electrowetting directly on conducting substrates was provided by Frumkin, who, following the predictions of Lippmann’s theory of electrocapillarity, demonstrated the striking effect of potential bias on the shape of an oil droplet in contact with a mercury electrode immersed in an aqueous electrolyte . The overall mechanism of the phenomenon for ideally polarizable interfaces (i.e., no faradaic reactions occur) is based on the decrease in the potential dependent solid–liquid interfacial surface tension upon application of a bias away from the potential of zero charge, E pzc , i.e., the potential at which the net charge at the electrochemical double layer (EDL) is zero (see Figure a) . More recently, in an attempt to decrease the energy demands presented in EWOD devices, Kornyshev and co-workers introduced, in a series of seminal studies, an alternative EWOC route based on immiscible electrolyte solutions. − In these studies, a sputtered gold film electrode was used, although significant wetting hysteresis was noted, resulting from its micron-scale roughness.…”

Structure and self-diffusivity of alkali-halide electrolytes in neutral and charged graphene nanochannels

“…[6][7][8][9][10][11] Under the extreme nanoscale confinement (o2 nm) found in these systems, confined aqueous electrolyte solutions offer unique structural and dynamical properties which drastically differ from those in the bulk phase. [12][13][14][15][16][17][18][19][20][21][22][23] The microscopic behaviour of water molecules and ions in the nanometre-sized channels of the graphene electrodes depends on a combination of energetic and entropic effects. 24 Energetically, it includes electrostatic interactions between the water molecules and ions, and the charge on graphene surfaces, ion-p interactions due to an abundance of aromatic rings with delocalised p-electrons, and electrostatic shielding due to reorientation of water molecules in the nanochannels and at their graphene surfaces.…”

“…The spatial distribution of the confined ions is then a result of interplay between the ions propensity to hydrate/dehydrate under confinement and the strength of the ion-graphene surface interactions mediated by confinement-induced layered water. 23,25 The spatial distributions of water molecules and ions in the graphene nanochannels have profound effects on their selfdiffusion behaviour. Under graphene nanoconfinements, the self-diffusion in three directions is restricted and confined species primarily diffuse along the graphene surface.…”

“…Aqueous electrolytes containing alkali metals (typically NaCl, KCl, and LiCl) have been used as model systems in experimental, theoretical and simulation studies of the electrochemical double layer at the graphene-aqueous electrolyte interface and aqueous electrolyte solutions in graphene nanoconfinements, see, e.g., recent reviews. 23,[49][50][51] For aqueous alkali-chloride electrolytes at both neutral and charged graphene surfaces, MD simulations predicted a strong, densely packed layered structure up to 1 nm from the graphene surface. The ions form a dense cation and anion layer each with the cations residing closer to the graphene surface than the chloride anions.…”